pi计算

计算pi

c语言版

#include <stdio.h>

int main() {
    int r[2800 + 1];
    int i, k;
    int b, d;
    int c = 0;

    for (i = 0; i < 2800; i++) {
        r[i] = 2000;
    }

    for (k = 2800; k > 0; k -= 14) {
        d = 0;

        i = k;
        for (;;) {
            d += r[i] * 10000;
            b = 2 * i - 1;

            r[i] = d % b;
            d /= b;
            i--;
            if (i == 0) break;
            d *= i;
        }
        printf("%.4d", c + d / 10000);
        c = d % 10000;
    }

    return 0;
}

gcc pi.c -o pi

用 shell 的 bc 命令计算很方便

   EXAMPLES
       In /bin/sh,  the following will assign the value of "pi" to the shell variable pi.
               pi=$(echo "scale=10; 4*a(1)" | bc -l)

测试记录

bash
time pi=$(echo "scale=10000; 4*a(1)" | bc -l)

# a is arctan, and this give pi to 10000 digits.

2022-01-13 MacBook Pro (14-inch, 2021) Apple M1 Max
real 0m50.483s
user 0m49.896s
sys 0m0.179s

2020-10-27 MacBook Pro (16-inch, 2019) 2.6 GHz 6-Core Intel Core i7
real 1m17.887s
user 1m17.080s
sys 0m0.184s

2020-11-21 Mac mini (2018) 3.2 GHz 6-Core Intel Core i7
real 1m8.796s
user 1m8.647s
sys 0m0.066s

2020-11-21 windows (WSL) centos7 AMD 锐龙5 3600X 处理器 (r5)7nm 6核12线程 3.8GHz 95W AM4接口 盒装CPU

yum install bc
real 1m16.686s
user 1m16.609s
sys 0m0.047s

2019? MacBook Pro (15-inch, 2017) 耗时 real 1m56.849s